Traveling grate apparatus with heat shielding

ABSTRACT

Traveling grate apparatus adapted to be subjected to severe and fluctuating elevated temperatures has supporting frame including metal supporting members, which members are substantially covered by metal shields secured to such supporting members with minimal contact areas, in order to provide heat insulating metal-to-air interfaces between the frame members and the shield to prolong the useful life of the frame.

United States Patent Inventor Tage Werner Rocky River. Ohio App]. No.810,624

Filed Mar. 26, 1969 Patented Feb. 2, 1971 Assignee Arthur G. McKee 8:Company Cleveland, Ohio a corporation of Delaware TRAVELING GRATEAPPARATUS WITH HEAT SHIELDING Primary Examiner-John J. CambyAztomeyBosworth, Sessions, Herrstrom and Cain ABSTRACT: Traveling grateapparatus adapted to be sub- 10 Claims 11 Drawing Figs jected to severeand fluctuating elevated temperatures has US. Cl 263/28, supportingframe including metal supporting members, which 266/21 members aresubstantially covered by metal shields secured to Int. Cl F27b 9/00,such supporting members with minimal contact areas, in order F27b 21/02to provide heat insulating metal-to-air interfaces between the Field ofSearch 266/21; frame members and the shield to prolong the useful lifeof the 2631/28, 50 frame.

4. 3/ e o K PATENTED FEB 2 um SHEET 3 OF 4 t 5 w mm g TRAVELING GRATEAPPARATUS WITH HEAT SHIELDING BACKGROUND OF THE INVENTION The presentinvention relates to re traveling apparatus of the type used fortreating at elevated temperatures materials such as iron ore, and moreparticularly it relates to traveling grate apparatus having metalsupporting members heat shielded to protect them against adverse effectsof severe and fluctuating temperatures.

While the invention is useful in a wide variety of treating apparatus,for convenience it will be discussed in connection with agglomeration ofparticulate materials such as particles of iron oxide. in which use itprovides particular advantages When agglomerating particulate ironoxide, it is the practice to heat the material on a traveling grateapparatus in which the material is passed through one or more heatingzones in which the heat applied to the material causes it to formhardened aggregates. In widely used pelletizing processes. particulatebeneficiated iron ore is first formed into moist green balls which arefirst heated on a traveling grate to dry them, and then subjected tohigh indurating temperatures while on such a grate to convert the ballsinto heat hardened iron ore pellets that can be shipped, stored and usedin blast furnaces; usually the pellets are also cooled while on thegrate to cool them to temperatures permitting their ready handling Suchheating and cooling on the grate causes temperature variations to whichthe grate is subjected, ranging from higher temperatures in the range of2200 F. to 2500 F. to lower tempera tures in the range of 300 F. to 600E. which variations subject the grate to severe thermal stresses.

Furthermore, many grates used in both pelletizing and sinteringprocesses are straight horizontal grates having an upper run on whichthe particulate material is subjected to the heating and if desiredcooling, and a lower return run in which the grate parts are subjectedto considerably lower ambient temperatures as they travel back to thebeginning of the upper run. This causes the grate parts to be exposed tolow temperatures and consequent variations between low temperatures andhigh temperatures and thermal shocks.

In both pelletizing and sintering apparatus the material on the grate issubjected to the various treating temperatures by hot gases passedthrough the grate, which has a permeable bottom for that purpose. Thepermeable bottom of such a grate in general comprises movable bars thatare held in a frame, spaces being provided between the bars over substantial portions of their length for passage of gases. The supportingmembers of the frame are subjected to the fluctuating temperaturesdescribed above.

The repeated drastic heating and cooling to which the frame members aresubjected for the above reasons, tend to cause them to deteriorate andto sag, warp, twist or otherwise distort. Such distorting can cause theframes to jam in their supports to an extent to prevent operation of thetraveling grate apparatus, or prevent desired removal and replacement ofgrate bars: the deterioration. moreover, can in time so weaken theframes as to cause them to fail.

In time, such deterioration or distortion becomes so great that theframe members must be replaced, which often requires shutdown of thetraveling grate apparatus with consequent loss of production during thetime required for replacement, and also involves substantial economiclosses because portions of the traveling grate must be discarded. Inlarge installations such losses could run into tens of thousands ofdollars. These tendencies are accentuated because of modern practiceswhich involve the use of higher temperatures and greater temperaturespreads.

Various attempts have been made to ameliorate these difficulties. Oftensuch attempts have involved making the frame members of the travelinggrate of expensive alloy steel castings rather than lower cost cast ironor ordinary steel castings. This involves greatly added cost over thecost of grates made of less expensive material. but still can eventuallyresult in the necessity for replacing grate portions because of thedistorted supporting members.

Other proposals have involved using grate frame members of specialdesign including those having massive supporting members, speciallyrecessed members. etcv While in U. S. Pat. No. 3.384355 it has beenproposed to provide heat shields resting on the upstanding sidewalls ofa traveling grate, applicant knows of no attempt to protect thesupporting members of the grate m which the tendencies to deteriorate ordistort are much more serious because of their direct exposures to hotgases. which are more complicated in structure and therefore presentdifferent and more difficult problems because of their complexities ofshapes, and when are load bearing and must include provision forsupporting the grate bars so they are securely held in place duringoperation of the grate but can be readily removed if desired.

SUMMARY OF the THE INVENTION According to the present invention, thesupporting members of a traveling grate have metal shields thatsubstantially cover, and preferably essentially completely cover, thesurfaces of the frames that are exposed to heat. These shields areattached to the frame with minimal contact; and preferably each shieldis attached in such a manner as to permit virtually free expansion andcontraction when exposed to heat. The shields are so mounted that theyprovide large metal-to-air in terfaces between the supporting membersand the shields, which provide heat insulation and which prolong theuseful life of the supporting members. If desired, superposed metalshields may be used over part or all of the supporting members.

DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrateembodiments of the invention in which:

FIG. I is a front elevation, partly in section, illustrating a type oftraveling grate pallet which can be beat shielded in accordance with thepresent invention:

FIG. 2 is an isometric view of the frame of the pallet of FIG. I andillustrates the relative positions of some of the metal shields, some ofwhich are shown in exploded view;

FIGS. 3 and 4 are plan and end elevations, respectively, of the palletframe of FIGS. 1 and 2;

FIGS. 5 through 8 are sections of FIG. 3 on the indicated section linescorresponding to the numeral of the figure;

FIG. 9 is a section of FIG. 4 on the line 9-9 with parts broken away forpurposes of illustration;

FIG. 10 is an end elevation of a pallet frame member having a modifiedform of shield, the shield being shown in section for purposes ofclarification; and

FIG. 11 is also an end elevation of a pallet frame member having amodified form of shield, the shield again being shown in section forpurposes of clarification.

DESCRIPTION OF THE PREFERRED EMBODIMENT For convenience, the inventionis discussed below in connection with pallets of a straight, generallyhorizontal traveling grate pelletizing apparatus. Such grate comprises anumber of abutting pallets, generally indicated at 1, each of which haswheels 2 that roll on rails 3. Each pallet has a gas-permeable hearthportion 4 and upstanding sidewalls 5 that, with corresponding parts ofabutting pallets, define a channel-shaped cross section in which thematerial 6 being heated is carried.

As shown in FIG. I each pallet comprises a frame 7 in which cast metalside beams 15 are bolted to sections 16 which are bolted, in turn, toplates 17, members 16 and I7 defining the upstanding sidewalls 5. Theside beams I5 are joined one to the other through the pallet frame andcarry the conventionally journaled wheels 2.

In the embodiment shown, the pallet framework comprises two integrallycast, identical, metal half-sections 20 and 21, of which one section 20is depicted in FIGS. 2-10. Each section has the same construction andcomprises an outer transverse member 22 having a longitudinal slot 23which mates with a similarly shaped projection 24 on a side beam of thepallet Four spaced. parallel supporting members extend from each member22 The outer two members 25 are identical. and the 5 inner two members26 are similar except for lip portions 27 which extend toward oneanother Spacedv parallel crossmenr bers 28 and 28a extend between themembers 25 and 26 to reinforce the pallet frame and usually are at lowerelevation 0 than the member 25 and 26. The innermost crossmembers 28a ofeach pallet section are bolted to each other to secure the two sectionstogether as a single unit.

A number of grate bars 30 are supported atop the members 25 and 26,point in a direction paralleling the sidewalls 5. andv s extend from onesidewall to the other (FIG. 1). In the embodiment illustrated, the gratebars 30 are of standard construction and have periodic necked-downwidths (not shown) to permit the passage of gases between bars. Thegrate bars 30 have conventional depending hooks 31 which extend underthe lip portions 27 of members 26 to hold the bars in place when thepallet is in material carrying position as shown.

In practice, the bars 30 immediately support the material 6 beingtreated. From FIGS. 1 and 2 it will be seen that the upper faces ofmembers 25 and 26 carry the grate bars. Crossmembers 28 and 280 are at alower elevation and do not contact the bars 30.

In the embodiment illustrated by FIGS. 1 through 10, all of the palletframe members have some heat shielding. As a general rule, only the topand side faces of a member are heat shielded because in this case thehottest gases to which the pallet is subjected pass downwardly throughthe material on the grate and through the grate in the indurating orsintering zone through which the grate passes; however, the extent ofareas shielded may differ. For example, members 22 have only the upperand inner faces shielded, so that the outer faces may mate with a sidebeam 15 as described. On the other hand, crossmembers 28 have all foursides heat shielded (FIG. 6). Further, members 25 ad and 26 are notshielded along their bottom faces (FIG. 7), since the heat exposure isnot as severe here. Also, these members repeatedly contact dead platesforming seals between separate treating zones and, if shielded, theshields would tend to tear from such repeated contact.

In general, the shields may be a of any suitable sheet material, such ascommon cold rolled steel, but they may be formed of alloy metal ifdesired. The shields are designed to fit about only relatively shortlengths of a frame member. A number of shields are then placed end toend, to cover a particular frame member as may be desired. Also indetermining the shape of a particular heat shield, the proximity of theshield to other members, projections, junctures of members to members,corners, etc. are taken into account in establishing the actual size andgeometric shape and design of the shield.

Ideally, a shield would float with respect to a protected 55 member,that is, there would be a continuous, uninterrupted air envelope betweenthe shield and memberv However, since some attachment between the shieldand member is necessary, the securing area preferably desirably ismaintained at a minimum. Preferably, each shield is secured by a singlefastening means which fixes essentially a point on the metal shield to aface of the metallic support member, as by spot welding, a bolt, or thelike. Further, where contact between the shield and a frame member isunavoidable, this contact is again preferably held to a minimum, as byspacing m: ms which holds the shield away from the member whilemaintaining a physical contact between the shield and member of minimumpracticable area. The reduced heat conductivity at the metalairinterface at each side of each shield provides considerable heatinsulation for the metal frame members, so that they 70 remain at lowertemperatures and in this manner are less susceptible to deterioration.

Referring specifically to the shapes of the shields used in theembodiment of FIGS. 1 through 10, the edge member 22 has inventedL-shaped shields 32 and 33 which cover the inner 75 and upperfaces ofthe member The outer face of member 22. must be free to butt against aside beam 15 The longer legs of the L-shaped shields 32 and 33 cover theinner face of member 22 as II'IdICil16d. while the shorter legs of theshields cover the top face Shield 33 is shorter than end shields 32,since edge member 22 is recessed at its medial section (FIGS. 2 and 6)Shields 32 have tabs 34 on their shorter legs which extend toward eachother and cover additional area atop the edge member 22.

All of the shields 32 and 33 have single fastening means in the form ofbolts 35 which pass through the shield, edge member 22. and the end beam15 at the juncture of the interfitting groove 23 and projection 24. Thesingle bolt fastening means includes a spacer 36. lock washer 37. andnut 38. The end shields 32 (FIG. 8) have strip spacers beneath theshorter legs which are fixed by welding to the shield. Alternatively,the strip spacers 40 could be fixed to the top face of the member 22. Ineither case, these spacers reduce the area of contact between theshorter legs of the shields 32 and member 22 and are in strip formbecause member 22 is load bearing.

The outer two members 25 of the pallet frame are similarly shielded, sothat only one is described in detail. The shields 41 for these members(FIGS. 3, 4, and 5) are all of inverted U- shape and have strip spacers42 beneath their bight portions. FIG. 9 illustrates a strip spacer 42and in general what is encompassed herein by that term. Preferably, astrip spacer corresponds in length to the length of the shield to whichit is attached in order to bear a load. but the strip spacer has areduced width as compared to width of the bight portion of the shield.The smaller area of the strip thereby reduces the conduction of heatthrough the strip. The bight section of the outermost shield 41 on eachmember 25 has a tab 43 which covers the end corner of the members. Theinner sides or legs of the U-shaped shields 41 have cutaway sectionsgenerally indicated by reference character 44 (FIG. 5) to accommodatecross members 28 and 28a. Single bolt connectors 45 pass through amember 25 from an inside face to join the leg portions of each shield 41(FIG. 7). The bolts have ring spacers 46, while the outer face of amember 25 has a recess matching the shape of a nut 47 for the bolt.

The inner two members 26 of the pallet frame are also similarlyshielded, so that only one is described in detail. In this casetwo-piece shields (FIGS. 3 and 7) are used. One of the pieces 48 has aninverted J-shape covering a side face of a member 26 with its larger legsection and extendinga turned end 50 to embrace the upper face of amember 26 as well as its lip portion 27. A strip spacer 51, such as theone illustrated in FIG. 9, lies beneath the turned end 50 and freelyseats against the upper face of a member 26. Another piece 52 cooperateswith piece 48 in covering a member 26. Piece 52 is planar with a rightangle edge turn which fits beneath a lip portion 27. Members 26 have asingle opening 53 for each shield through which a bolt-nut combination54 passes to secure the pieces 48 and 52 relatively to eachother and toa member 26. The bolt has a spacing collar 55 and a washer 56.

It will be appreciated that in FIGS. such as FIG, 7, the thickness ofthe shields has been exaggerated for purposes of illustration. Actually,it is the heat insulating properties of the air-metal interface on eachside of a shield that is important in providing protection from heatrather than the thickness of the shield. The shield can be as thin aspractical as long asit is selfsupporting and avoids warping. Referringto the center of FIG. 7, it will be noted that spacing collars are notnecessarily used. Spacing collar 55 is used between shield 48 and member26 in the center of FIG.,7, but none is used on the opposite sidebetween shield 52 and the member. In cast metal parts, such as themember 26, the natural roughness and surface irregularities of thecasting inherently result in spacing of a shield. This minimizesappreciable metal-to-metal contact'and does provide a substantialair-to-metal interface.

All four faces of the crossmembers 28 are heat shielded by twotelescoping U-shaped sections 57 and 58 (FIG. 6). The upper section 57is shorter, overlaps the lower section 58and is welded thereto along theends of its legs. Strip spacers 60 (FIGS. 3 and 6) fit between the hightportion of section 57 and the top face of a member 28 and preferably arenot fixed with respect to either part. The innermost crossmembers 28aare at a somewhat lower elevation than crossmembers 28 (FIG. 6) and haveinverted U-shaped heat shields 59 These shields have bight portions ofsufficient length to bridge two such crossmembers in order to unitehalf-section 20 of the pallet frame to identical half-section 21 andform a single unit (FIG. 1 FIG. 6 illustrates in phantom the cooperatingcrossmember 28b of a companion framework. A strip spacer 61 beneath thebight section of a shield 59 rests upon both of the joined cross members28a and 28b. These members have aligned openings to accommodate abolt-nut combination 62 having spacers 63. In this instance, it may beadvisable, as shown, to have two of such bolts for each shield 59 andprotect members 28a and 28b in order to provide a sufficiently strongconnection between the two similar frames defining the pallet.

FIGS. and 11 illustrate two modifications of the present heat shielding.In certain installations. parts of the pallet framework may be moreseverely exposed to heat than other parts. In this case, a number ofsuperposed metallic shields may be used, preferably with the same singlefastening and with spacing means. For example, in FIG. II a frame member64 has two inverted U-shaped shields 65 and 66 successively placedaround it. Spacing means 67 separates the top face of member 64 and thebight portion of shield 65. and spacing means 68 separates the bightportion of shield 65 from that of shield 66. To secure shields 65 and 66to the member 64, a sin gle bolt and nut combination 68 may be used.Preferably the bolt has spacers 70 interleaved between the shields 65and 66 and a lock washer 71. The severest heating conditions usuallyoccur at the top of the frame members and therefore the embodiment ofFIG. 10 can be especially advantageous.

The embodiment of FIG. 11 is similar to that of FIG. 10, except that aninner shield 72 is much thinner than shield 65 and has legs corrugatedor dimpled as at 73. It will also be noted that the embodiment of FIG.10 omits spacers for the bolt such as the spacers 70 of FIG. 10. Theremaining parts are similar to those of FIG. 10 and have, therefore,been indicated by like numerals.

If desired, one or more of the heat shields may have a highly reflectivesurface. This increases the insulating effect by adding heatreflectivity to the reduction in heat conductivity provided by theair-metal interfaces. By means of the present shields the range offluctuating temperatures is narrowed, so that there is less thermalvariance and shock on the frame and its attendant parts. The shieldstend to stabilize the temperatures by reducing both the abruptness andmagnitude of changes in temperature to which the frame members of thegrate are exposed.

It is understood that frame members heat shielded in accordance with thepresent invention, may support grate members of traveling straightgrates or traveling circular grates.

While the foregoing describes several embodiments of the invention. itis understood that other modifications may be made within the scope ofthe following claims.

lclaim:

I. In traveling grate apparatus having a moving grate and including aframe that is subjected to severe and fluctuating temperatures and thatcomprises at least one metal supporting member. a metal shieldsubstantially covering the surface of said supporting member that wouldotherwise be exposed to heat and having a minimal attachment to themember to provide a metal-air interface adjacent said supporting memberof substantial area that substantially reduces heat transferred to saidmember substantially to reduce deterioration of the member by heat andto prolong useful life of said member, wherein said minimal attachmentincludes fastening means that permits substantially unrestrainedmovement of said shield relative to said supporting member duringthermal expansion and contraction thereof while maintaining saidmetalair interface between said shield and supporting member.

2. The apparatus of claim 1 wherein said minimal attachment includessingle fastening means securing essentially a point of the metal shieldto a face of the metal supporting member.

3. The apparatus of claim 1 including spacing means interfitted betweenthe metal shield and a face of the metal supporting member and effectiveto aid in forming said metal-air interface.

4. The apparatus of claim 3 wherein said spacing means is in strip form.

5. The apparatus of claim 3 wherein said interfitted spacing means isnot fixedly secured to either the shield or support member.

6. The apparatus of claim 1 wherein at least one section of said shieldis corrugated.

7. The apparatus of claim 1 wherein a plurality of superposed metalshields cover said interconnecting metal supporting member, each metalshield having an insulating metal-airmetal interface with its contiguouscompanion shield.

8. The apparatus of claim 7 wherein all of the metal shields have acommon attaching means securing the shields to a metal supportingmember.

9. Grate apparatus adapted to be subjected to severe and fluctuatingtemperatures having a frame to support a load, said frame comprisingspaced-apart metal members held in fixed relation by spaced-apartcrossmembers, a strip spacer on a face of said members, a metal shieldfitted over members and resting upon said strip spacers, and singlefastening means securing essentially a point of each shield to itsprotected support member.

10. The apparatus of claim 9 wherein said crossmembers are at a lowerelevation than said metal members.

1. In traveling grate apparatus having a moving grate and including aframe that is subjected to severe and fluctuating temperatures and thatcomprises at least one metal supporting member, a metal shieldsubstantially covering the surface of said supporting member that wouldotherwise be exposed to heat and having a minimal attachment to themember to provide a metal-air interface adjacent said supporting memberof substantial area that substantially reduces heat transferred to saidmember substantially to reduce deterioration of the member by heat andto prolong useful life of said member, wherein said minimal attachmentincludes fastening means that permits substantially unrestrainedmovement of said shield relative to said supporting member duringthermal expansion and contraction thereof while maintaining saidmetal-air interface between said shield and supporting member.
 2. Theapparatus of claim 1 wherein said minimal attachment includes singlefastening means securing essentially a point of the metal shield to aface of the metal supporting member.
 3. The apparatus of claim 1including spacing means interfitted between the metal shield and a faceof the metal supporting member and effective to aid in forming saidmetal-air interface.
 4. The apparatus of claim 3 wherein said spacingmeans is in strip form.
 5. The apparatus of claim 3 wherein saidinterfitted spacing means is not fixedly secured to either the shield orsupport member.
 6. The apparatus of claim 1 wherein at least one sectionof said shield is corrugated.
 7. The apparatus of claim 1 wherein aplurality of superposed metal shields cover said interconnecting metalsupporting member, each metal shield having an insulatingmetal-air-metal interface with its contiguous companion shield.
 8. Theapparatus of claim 7 wherein all of the metal shields have a commonattaching means securing the shields to a metal supporting member. 9.Grate apparatus adapted to be subjected to severe and fluctuatingtemperatures having a frame to support a load, said frame comprisingspaced-apart metal members held in fixed relation by spaced-apartcrossmembers, a strip spacer on a face of said members, a metal shieldfitted over members and resting upon said strip spacers, and singlefastening means securing essentially a point of each shield to itsprotected support member.
 10. The apparatus of claim 9 wherein saidcrossmembers are at a lower elevation than said metal members.